Conventionally, small-sized blades such as turbine blades, paddle blades, and propeller blades are often used as agitation blades of an agitation apparatus to process fluids with low to middle viscosities. To process fluids with middle to high viscosities, anchor blades or helical ribbon blades are often used as the agitation blades.
However, it has been known that small-sized blades easily produce a flow boundary in an agitation vessel, which not only hampers generation of a vertically circulating flow throughout the vessel but also causes insufficient mixing when fluid with high viscosity is processed. Contrastingly, as has been known, the anchor blades or the ribbon blades cause insufficient mixing due to simultaneous revolution when fluid with low viscosity is processed.
Particularly, when the small-sized blades are employed to agitate a highly thixotropic fluid, the fluid is flowable only in the proximities of the blades but not in ranges spaced from the blades, which are the vicinities of the inner wall and the bottom portion of the agitation vessel, thus causing insufficient mixing. The anchor blades and the ribbon blades, which are arranged along the inner wall of the agitation vessel, ensure fluid flowability in the vicinities of the vessel wall and at the vessel bottom portion but cancel the flowability in a central portion of the agitation vessel. Also in this case, mixing becomes insufficient.
Accordingly, the aforementioned agitation blades all increase risks of insufficient mixing and incomplete reaction when such a chemical reaction that the viscosity of a substance to be processed greatly changes is brought about in the agitation vessel or a highly thixotropic substance to be processed is mixed and caused to react in the agitation vessel.
To solve this problem, as illustrated in FIGS. 29 to 31, an agitation apparatus 21 (see Patent Document 1) having upper blade sets 24 and lower blades 25 has been proposed. The upper blade sets 24 are inclined at elevation angles with respect to the rotating direction of an agitation shaft 23. The lower blades 25 are each arranged vertically (along the axial direction of the agitation shaft 23).
Each of the upper blade sets of the agitation apparatus are configured by arranging a first upper agitation blade 26a and a second upper agitation blade 26b, which are formed in quartered oval shapes, in such a manner that the first agitation blade 26a extends parallel to the second upper agitation blade 26b and a lower portion of the first upper agitation blade 26a is overlapped with an upper portion of the second upper agitation blade 26b, thus forming as an inclined and stepped semi-oval blade set 24. A pair of such inclined and stepped semi-oval blade sets 24 (the first upper agitation blades 26a and the second upper agitation blades 26b) are inclined upward with respect to the rotating direction of the agitation shaft 23 and fixed to the agitation shaft 23 in such a manner as to be located on opposite sides of the agitation shaft 23.
Each of the lower blades 25 is formed as a flat plate having an outer peripheral end extending to the proximity of a vessel wall. A distal portion (an outer peripheral end portion) of each lower blade 25 is bent rearward with respect to the rotating direction of the agitation shaft 23 (in the opposite direction to the rotating direction of the agitation shaft).
When the agitation blades are configured in the above-described manner, rotation of the agitation shaft 23 integrally rotates the inclined and stepped blade sets 24, which are attached to the agitation shaft 23. In this state, the fluid in an upper portion of the vessel is sent downward (toward the bottom) from the vicinity of an upper portion of each inclined and stepped blade set 24 (the proximity of a fluid level) along the inclined and stepped blade set 24. In this manner, the fluid in the upper portion of the vessel is displaced to a lower portion of the vessel (toward the lower blades 25). The fluid is then agitated radially outward in the vessel by the lower blades 25 and strikes the vessel wall, which sends the fluid upward, thus forming a vertically circulating flow in the vessel. As a result, fluids (liquids) with a wide spectrum of viscosities from low to high levels are agitated and mixed in a vertical direction.
As illustrated in FIGS. 32 to 34, an agitation apparatus 31 including upper blade sets 34, which are attached to an agitation shaft 33, and lower agitation blades 35 formed as flat plates, has been proposed (see Patent Document 2). The lower agitation blades 35 extend downward from the vicinities of the lower ends of the upper blade sets to the vicinities of the bottom surfaces of the vessel, projecting radially outward from the agitation shaft. Each of the upper blade sets 34 includes a set of upper agitation blades 36 at a plurality of levels, which are configured by arranging the upper agitation blades along a circumferential direction of the agitation shaft 33 to be spaced apart at predetermined intervals and inclining the upper agitation blades by a predetermined elevation angles with respect to the rotating direction of the agitation shaft. Corresponding ones of the upper agitation blades 36 at all levels are arranged at such positions that a highest upper agitation blade and a lowest upper agitation blade are axially overlapped with each other in such a manner that a lower side portion of the highest upper agitation blade is visible from a lower side portion of the lowest upper agitation blade. The angle about the agitation shaft between an upper side of a highest upper agitation blade and a lower side of a lowest upper agitation blade with respect to the rotational direction is less than 180°.
When the agitation blades are configured in the above-described manner, rotation of the agitation shaft 33 causes the upper blade sets 34 to move the liquid in an upper portion of the vessel toward the lower blades 35 (a lower portion of the vessel). The rotation angle of the agitation shaft 33 necessary for such movement is less than 180°. Accordingly, the fluid (the liquid) in the upper portion of the vessel is rapidly sent to the lower portion (the bottom portion) of the vessel by the small rotation angle.
Further, as illustrated in FIGS. 35 to 37, an agitation apparatus 41 having upper blade sets (auxiliary agitation blade sets) 44 and flat plate-like lower blades (main agitation blades) 45 has been proposed (see Patent Document 3). Each of the upper blade sets 44 includes scrapers and paddles. Each of the scrapers is arranged at a side of the upper blade set 44 corresponding to an inner wall of an agitation vessel and inclined in such a direction that the scraper scrapes up a substance to be processed with respect to the rotating direction of an agitation shaft 43. Each one of the paddles is connected to the corresponding one of the scrapers and inclined in such a direction that the paddle presses down the substance to be processed when rotation occurs. The lower blades 45 are arranged at the lowermost level of the agitation shaft.
Each upper blade set 44 of this agitation apparatus is configured by upper agitation blades at a plurality of levels, which are, for example, as illustrated in FIGS. 35 to 37, a highest upper agitation blade 46a, a middle upper agitation blade 46b, and a lowest upper agitation blade 46c. The scrapers, which are formed substantially in T shapes, are attached to the upper agitation blades 46a, 46b, 46c at the sides corresponding to the inner wall of the agitation vessel. The clearance between the inner wall surface of the vessel and the outer peripheral portion of each scraper is small. In each vertically adjacent pair of the upper agitation blades, the upper end of the upper agitation blade at a higher position is arranged in such a manner as to produce a phase difference with respect to the lower end of the upper agitation blade at lower position in the opposite direction to the rotating direction of the agitation shaft 43.
Each of the lower blades 45 is arranged in such a manner that the outer peripheral portion of each blade is spaced from the inner wall surface of the agitation vessel and that the lower blade 45 is located at the lowermost level of the agitation shaft. The upper end of each lower blade 45 is arranged in such a manner as to generate a phase difference with respect to the lower end of the corresponding lowest upper agitation blade, which is located adjacent to and above the lower blade 45, in the opposite direction to the rotating direction of the agitation shaft 43.
In the agitation apparatus 41 configured as described above, rotation of the agitation shaft 43 rotates the upper blade sets 44 and the lower blades 45, which are attached to the agitation shaft 43. In this state, the scraper portions of the upper agitation blades move the substance to be processed in the vicinity of the inner wall of the agitation vessel in an upward direction in scraping manners. Also, the inclined paddles, which are arranged inward from and connected to the scrapers, move the substance in the vicinity of the center of the agitation vessel in a downward direction toward the lower blades 45 in depressing manners. Then, the lower blades 45, which are located in the vicinity of the bottom portion of the agitation vessel, send the substance radially outward in the vessel, thus forming vertically circulating flows. As a result, fluids (liquids) with high viscosity and high thixotropy are efficiently agitated and mixed together.    Patent Document 1: Japanese Laid-Open Patent Publication No. 09-75699    Patent Document 2: Japanese Laid-Open Patent Publication No. 2007-90265    Patent Document 3: Japanese Laid-Open Patent Publication No. 06-170202